Diagnostic article Generic OBD-II
P2536: Transmission controller sees accessory input disagree with power mode
Understand the accessory-input mismatch behind this GM P2536 monitor and why a working ignition circuit does not rule it out.
Read before applying this article
Documented application
GM 2009 09OBDG01 GMDAT transmission diagnostics, accessory-input monitor on physical page 9. Network identifiers and input-state timing are calibration-specific; per-vehicle applicability is not established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P2536 concerns the ignition accessory circuit, but the cited GM transmission controller reaches that conclusion by comparing power-state information. It detects its accessory input off while the network power-mode master reports the accessory terminal active and the controller sees ignition on.
Two power inputs are not interchangeable
The engine can be running and the ignition input can be present while the accessory input disagrees. In this calibration, engine speed above 400 rpm and battery voltage between 10.2 V and 15.5 V are among the enabling conditions. A successful engine start therefore does not independently verify the monitored accessory path.
GM labels the fault as an open accessory line. The summary does not identify a specific wire, fuse, switch contact or connector, so that classification is evidence for vehicle-specific circuit diagnosis rather than proof that the ignition switch assembly needs replacement.
The network comparison must be trustworthy
The monitor requires no CAN bus-off or body-controller communication failure. If the network power-mode message is unavailable, the intended comparison is not equivalent to a valid “accessory active” report. Preserve communication faults and actual power-mode data alongside the transmission controller's discrete input state.
The table describes qualified input-state timing and a 20-failure decision, with no MIL for this Special Type C entry. An absent engine warning lamp therefore does not establish that the accessory monitor passed. Verification should reconcile the controller's input with the power-mode master's report under the correct operating sequence; the historical summary does not establish vehicle fitment or a universal switch test.
Source and applicability
GM 2009 09OBDG01 GMDAT transmission diagnostics, accessory-input monitor on physical page 9. Network identifiers and input-state timing are calibration-specific; per-vehicle applicability is not established.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Ignition Switch Accessory Position Circuit
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT